Measuring and testing – With fluid pressure
Reexamination Certificate
1999-03-22
2003-03-18
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
C361S234000, C118S72300R, C118S724000, C118S728000, C156S345420, C279S128000
Reexamination Certificate
active
06532796
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a method of substrate temperature control, and a method of assessing substrate temperature controllability in a substrate processing apparatus, and in particular it concerns a method of controlling the substrate temperature which can be used in a substrate processing apparatus in which a substrate is held on a substrate holder by means of an electrostatic force and a heat transfer gas for substrate cooling purposes is passed between the substrate and the electrostatic chucking stage, and a method of assessing the controllability of the substrate temperature.
2. Description of Related Art
A conventional method of substrate temperature control in a plasma processing apparatus is described below with reference to FIG.
4
and FIG.
5
. Any plasma source can be used in this plasma processing apparatus, and it is not shown in the drawing. In the drawings, reference number
101
is the process chamber, and the construction of its upper part is not shown in the drawing. A substrate holder
102
is arranged in the bottom part of the process chamber
101
, and a substrate
103
is arranged on the substrate holder
102
. The substrate
103
is held by means of an electrostatic chucking stage
104
. The substrate holder
102
comprises a bias electrode
105
and a circulator
106
, which circulates a cooling medium which cools the electrostatic chucking stage
104
. A substrate bias electrode radio frequency power source
107
and a direct current power source
108
are connected to the bias electrode
105
.
A gap is formed between the substrate
103
and the electrostatic chucking stage
104
. An inert gas, such as helium (He) gas for example, is supplied into this space by means of a pipe
109
. He gas is present and functions as a heat transfer gas, which enhances the thermal transfer characteristics between the substrate
103
and the electrostatic chucking stage
104
and cools the substrate
103
. Moreover, reference number
110
is a conventional helium pressure control apparatus and reference number
111
is an evacuation pump which exhausts the He gas. The pressure of the aforementioned He gas is controlled by means of the helium pressure control apparatus
110
and the evacuation pump
111
. The helium pressure control apparatus
110
comprises a helium pressure controller
112
, a pressure gauge
113
, a mass flow controller
114
, valves
115
and
116
, and a bypass valve
117
.
The substrate
103
which is held on the substrate holder
102
by an electrostatic force is subjected to an etch process with the plasma which is generated by the plasma source. During this process, a radio frequency (RF) is applied to the bias electrode
105
from the RF power source
107
, and a self bias voltage is generated at the surface of the substrate
103
. A direct current (DC) voltage is applied from the DC power source
108
, and an electrostatic force is generated by the potential difference between the DC voltage and the self bias voltage, and this holds the substrate
103
.
The method of controlling the He gas pressure is described below. Thus, He gas pressure control is achieved by means of the helium pressure controller
112
. The helium pressure controller
112
sends a set flow-rate value via a signal line
118
to the mass flow controller
114
and recognizes the measured pressure which is sent from the pressure gauge
113
via a signal line
119
. Thus, the helium pressure controller
112
sends open or close signals via a signal line
120
when the measured pressure is displaced from the set pressure value, the bypass valve
117
is opened or closed, and the He gas pressure is controlled.
This is described in more detail below with reference to FIG.
5
. When the substrate
103
is not being etched, the valve
115
is closed, the bypass valve
117
is open and the valve
116
is closed. Moreover, the set He gas flow rate of the mass flow controller
114
is set to 0 sccm, and the set pressure value for the He gas is 0 Torr. The He gas pressure control which is carried out during the etch process of the substrate
103
starts after the substrate bias electrode RF power source
107
has been switched ON. At this time, the valve
115
is switched from closed to open, the bypass valve
117
is switched from open to closed, and the valve
116
is switched from closed to open. For pressure control, a set flow rate value signal for 20 sccm He gas is sent from the helium pressure controller
112
to the mass flow controller
114
, and the He gas pressure is brought up to the set pressure value of 15 Torr.
With this pressure control, no He gas flows after the He gas measured pressure value has reached the set pressure value. A small amount, for example some 0.5 sccm, of He gas leaks into the space inside the process chamber
101
from between the substrate
103
and the electrostatic chucking stage
104
. The measured He gas pressure falls below the set pressure value. He gas in an amount slightly greater than the amount which is leaked out, for example 0.6 sccm, is passed, and a fall in the measured He gas pressure is prevented. When the pressure exceeds the set pressure value, by 5 Torr for example, the bypass valve
117
is opened and He gas is exhausted with the evacuation pump
111
until the measured He gas pressure reaches the set pressure value of 15 Torr. The bypass valve
117
is closed again when the measured pressure reaches the set pressure value. Subsequently, the operation of the region indicated by
121
in
FIG. 5
is repeated and the He gas pressure is controlled until the RF power source
107
is switched OFF. With this pressure control, the valve
116
is switched from open to closed and the bypass valve
117
is switched from closed to open at the same time as the RF power source
107
is switched OFF. Moreover, the set flow rate of the mass flow controller
114
is set to 0 sccm and the set pressure value is set to 0 Torr. The He gas between the substrate
103
and the electrostatic chucking stage
104
is exhausted for a fixed period of time with the evacuation pump
111
, and then the valve
115
is switched from open to closed.
OBJECTS AND SUMMARY
In the conventional method of He gas pressure control, the control of He gas pressure during the interval
121
shown in
FIG. 5
is carried out simply by opening and closing the bypass valve
117
. However, fine control of the He gas pressure between the substrate
103
and the electrostatic chucking stage
104
by simply opening and closing the bypass valve
117
is very difficult in practice. The variability in the change in the measured pressure with respect to the set pressure value is considerable. As a result, a variability arises in the substrate temperature from substrate to substrate when substrates
103
are continually being subjected to an etch process. Such a variability of the substrate temperature results in a variability between substrates in the selectivity to the mask and the selectivity to the underlying layer which are sensitive to changes in the substrate temperature. As a result, the reproducibility of the etch profile is poor.
In general plasma processing apparatus with which etching is carried out, by-products which are formed during the etching process become attached to the electrostatic chucking stage as many substrates are etched repeatedly, the state of chucking between the substrate and the electrostatic chucking stage becomes inadequate and so the cooling of the substrate becomes inadequate and the substrate temperature rises. If the substrate etch process is carried out at a high temperature, then a problem arises in that the reproducibility of the etch profile becomes poor. In terms of this problem, execution of the etch process at high temperatures can be avoided if the etch process which is being carried out continuously is stopped when the state of chucking between the substrate and the electrostatic chucking stage becomes poor. However, with the conventional plasma processing apparatus described a
Anelva Corporation
Burns Doane , Swecker, Mathis LLP
Cygan Michael
Williams Hezron
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